Sen. Charles Schumer is so confident of re-election that he is steering millions from his campaign coffers to shore up other Democrats so he can become the Senate majority leader.

Already chosen by his party to replace retiring leader Sen. Harry Reid, of Nevada, Schumer has taken personal responsibility to elect like-minded senators across the country with about $8 million from his campaign and joint fundraising accounts.

Schumer, 65, typically talks to six Senate candidates a day on an old flip phone that colleagues tease has become molded to his hand.

“I’m strategizing. You come to my house and I’m looking at ads at 1 o’clock in the morning,” Schumer told The Post.

Democrats have to pick up four seats to take the majority. Two gains seem likely, in Wisconsin and Illinois. Schumer is also working to ensure wins in Senate races in Pennsylvania, North Carolina, Indiana, Florida and Missouri.